Enitaxial MnAs and Mn1xe2x88x92x NixAs thin films have been grown on semiconductors, such as GaAs (001) substrates with thicknesses of 20xcx9c200 nm. Magnetic, magneto optical and structural properties for x=0, 0.1, 0.2 and 0.3 were studied. As Ni is added to MnAs, the longitudinal magneto optical Kerr effect (MOKE, in-plane magnetization) becomes weaker and the polar Kerr effect (perpendicular magnetization) becomes distinct and disappears at x=0.3. Vibrating sample magnetometer measurements show that magnetization of the alloy film decreases linearly with Ni composition increase. X-ray diffraction results also show hexagonal and orthorhombic phases and a linear decrease of the ferromagnetic hexagonal phase fraction of the films wrath Ni composition increase. Therefore, the alloy film is considered to have a uniform distribution of hexagonal and orthorhombic phases. These results are clearly different from the bulk alloys of the same nominal compositions.
MOKE study of 20 nm MnAs/Gas thin films in perpendicular electric fields shows a decrease of Kerr signal when the substrate is at positive polarity relative to the surface. The electric field effect on the magnetization was measured using vibrating sample magnetometry (VSM) in electric fields. Electric field effects using VSM were largest in 20 MnAs films, smaller in 50 nm films and not observed in thicker films, indicating these effects arise from the substrate region of the MnAs. These films have some paramagnetic orthorhombic phase believed located in the region near the substrate. X-ray diffraction results show that the ferromagnetic hexagonal x-ray peak area decreases in both negative and positive electric field. The orthorhombic peak area does not change. Thus, the imposition of an electric field clearly either changes the phase composition or rotates the hexagonal structure from its original orientation.